# USRPN210 and Matlab problem in running the QPSK demo **URL:** \ **Category:** GNU Radio\ **Created:** [November 30, 2011, 6:31pm UTC](https://www.ruby-forum.com/t/usrpn210-and-matlab-problem-in-running-the-qpsk-demo/214386 "2011-11-30T18:31:29Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![dubstep](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/cdc98d/32.png) [@dubstep](https://www.ruby-forum.com/u/dubstep)\ **Post date:** [November 30, 2011, 6:31pm UTC](https://www.ruby-forum.com/t/usrpn210-and-matlab-problem-in-running-the-qpsk-demo/214386/1 "2011-11-30T18:31:29Z")
Dear all, having struggled for a couple of days with some new N210s I decided to post my problem in here. We recently received two N210s, which I am willing to interface with Matlab since the drivers have now officially been released and can be found in: > **[USRP Support from Communications Toolbox](https://it.mathworks.com/hardware-support/usrp.html)** > > Design and prototype software-defined radio (SDR) systems using USRP. I have burned the images for the firmware and FPGA on both USRPs. I have also installed MatlabR2011b on the two computers and configure it so that it can actually see the devices. I basically have two PCs and two N210s. Each PC has its own USRP. I attempted to run the QPSK demo TX/RX. However, I cannot decode the “Hello World” successfully in all cases. In fact, while the transmitter keeps running, the receiver stops and simply outputs the decoded message at Matlab’s command line. Here is what I see at the command line at the RX side, directly after I click on Simulation–\>Start in the sdruqpskrx simulink block: Opening a USRP2/N-Series device… ---------- end libuhd status message output ---------- ---------- begin libuhd status message output ---------- Current recv frame size: 1472 bytes ---------- end libuhd status message output ---------- ---------- begin libuhd status message output ---------- Current send frame size: 1472 bytes ---------- end libuhd status message output ---------- ---------- begin libuhd warning message output ---------- Unable to set the thread priority. Performance may be negatively affected. Please see the general application notes in the manual for instructions. EnvironmentError: OSError: error in pthread\_setschedparam ---------- end libuhd warning message output ---------- I have searched for this error but have not fully understood yet how to remove it. After compilation and if set Rapid Acceleration mode the following error comes up, and the simulation stops: “Unable to find an unused TCP/IP port to connect to the rapid accelerator target for model ‘sdruqpskrx’” However, if we set it to Acceleration mode then the simulation proceeds normally, but after a small period of time (not greater than 3-4 seconds) the simulation at the receiver stops and at the command line we get the decoded word. Below is just a short part of it: Hello world 052 Hello world 053 Hello world 054 Hello world 055 Hello wU|y 056 S\>,hd&/DF g6S B#WpP0rEW$YLK ello woHld 059 Hello world 060 Hello world 061 What we would expect however, is a continuous reception and attempt to decode the message at the RX side, since TX is constantly transmitting. It still puzzles me why the receiver cannot keep up at first place and of course why the message is not decoded successfully in all cases (distance between the units is very small). Also the frequency offset is in the order of 1KHz which can be compensated with this receiver configuration (can deal with offsets up to 12.5 KHz). Finally, I have varied numerously the gain parameter at the TX and RX but have not managed to decode the message successfully at all times. I apologize for the rather long post but I have made my best to describe the problem as compactly as possible. Thanks for your time in reading this. BR, Konstantinos ---
**Author:** ![tecne2003](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/b487fb/32.png) [@tecne2003](https://www.ruby-forum.com/u/tecne2003)\ **Post date:** [September 22, 2014, 5:27pm UTC](https://www.ruby-forum.com/t/usrpn210-and-matlab-problem-in-running-the-qpsk-demo/214386/2 "2014-09-22T17:27:55Z")
Hi valeris, I am working with this example at the moment, and I would like to know what you did to solve the problem. Furthermore, were you able to modify this example in anyway?